Laser communications following an atmospheric event

ABSTRACT

Systems, methods, and apparatus for laser communications following an atmospheric event. In one or more embodiments, the disclosed method involves transmitting, by at least one laser on at least one first satellite, at least one first transmit signal. The method further involves receiving, by at least one detector on at least one first satellite, at least one first receive signal. In one or more embodiments, at least one first satellite is in super-geosynchronous earth orbit (S-GEO). In at least one embodiment, at least one first transmit signal and at least one first receive signal are laser signals. Further, the method involves adapting, by at least one first processor on at least one first satellite, at least one first transmit signal according to at least one atmospheric event.

FIELD

The present disclosure relates to laser communications. In particular,it relates to laser communications following an atmospheric event.

BACKGROUND

Strategic nuclear forces have unique communications requirements, whichare: (1) global coverage, (2) near 100% availability, (3) long lifetime,(4) low probability of detection/interception (LPI/LPD), (5) able tooperate without ground intervention, (6) capable of working throughchallenging atmospheric environments, (7) capable of working throughpost-nuclear atmospheric effects, (8) resilient to manmade and naturalthreats, and (9) providing against natural threats, such as Van Allenradiation belts, solar storms, and geomagnetic storms.

Currently, there are a number of communications systems employed andbeing developed. However, these systems do not meet all of therequirements. These systems include, but are not limited to, theMilitary Strategic and Tactical Relay (Milstar) communicationsnetwork/Advanced Extremely High Frequency (AEHF) satellite system, theLunar Laser Communications Demo (LLCD), the Laser CommunicationsResearch Demo (LCRD), and the European Data Relay System (EDRS).

Regarding Milstar/AEHF, AEHF satellites are expensive. In addition,since AEHF satellites are in geosynchronous Earth orbit (GEO), they areeasy to detect and track.

LLCD demonstrated laser communications between the Earth and the Moon.LLCD's space element was placed into lunar orbit and was designed torelay scientific data from the Moon to the Earth. Although lasercommunications is inherently LPI/LPD, and the lunar orbit provides someresiliency to threats, LLCD does not provide global coverage, highavailability, long lifetime, or the ability to operate without groundintervention.

LCRD is a planned GEO satellite being developed by the NationalAeronautics and Space Administration (NASA) as a laser communicationstechnology demonstration. However, LCRD is to be located in and easilydetectable GEO and does not provide global coverage, high availability,long lifetime, or the ability to operate without ground intervention.

EDRS is a planned GEO-based satellite system being developed by theEuropean Space Agency (ESA) that utilizes an optical crosslink betweentwo satellites. EDRS does not provide global coverage, highavailability, long lifetime, or the ability to operate without groundintervention.

As such, there is a need for an improved communications system that isable to meet all of the strategic nuclear forces requirements.

SUMMARY

The present disclosure relates to a method, system, and apparatus forlaser communications following an atmospheric event. In one or moreembodiments, a method for communications involves transmitting, by atleast one laser on at least one first satellite, at least one firsttransmit signal. The method further involves receiving, by at least onedetector on at least one first satellite, at least one first receivesignal. In one or more embodiments, at least one first satellite is insuper-geosynchronous earth orbit (S-GEO). In at least one embodiment, atleast one first transmit signal and at least one first receive signalare laser signals. Further, the method involves adapting, by at leastone first processor on at least one first satellite, at least one firsttransmit signal according to at least one atmospheric event.

In one or more embodiments, at least one atmospheric event is a naturalevent or a manmade event. In at least one embodiment, the natural eventis a solar flare. In some embodiments, the manmade event is anelectromagnetic pulse (EMP).

In at least one embodiment, at least one first transmit signal employsinterleavers, and the interleavers are adaptable according to at leastone atmospheric event.

In one or more embodiments, at least one first transmit signal employscodecs, and the codecs are adaptable according to at least oneatmospheric event.

In at least one embodiment, a data rate of at least one first transmitsignal is adaptable according to at least one atmospheric event.

In one or more embodiments, at least one first transmit signal ismodulated, and a modulation format of at least one first transmit signalis adaptable according to at least one atmospheric event.

In at least one embodiment, the method further involves monitoring, withat least one first processor on at least one first satellite, linkperformance (a bit error rate and/or a signal strength) of at least onereceive signal and/or radiation data. The method further involvesdetermining, with at least one first processor on at least one firstsatellite, whether at least one atmospheric event has occurred using thelink performance (the bit error rate and/or the signal strength) and/orthe radiation data.

In one or more embodiments, the method further involves monitoring, withat least one second processor associated with at least one user, linkperformance (a bit error rate and/or a signal strength) of at least onetransmit signal and/or radiation data. The method further involvesdetermining, with at least one second processor associated with at leastone user, whether at least one atmospheric event has occurred using thelink performance (the bit error rate and/or the signal strength) and/orthe radiation data.

In at least one embodiment, the method further involves receiving, by atleast one user, at least one first transmit signal. In some embodiments,more than one user (i.e. two or more users) are separated by spatialseparation. In one or more embodiments, more than one user are separatedby spectral separation. In at least one embodiment, more than one userare separated by polarization separation. In some embodiments, more thanone user are separated by temporal separation. In one or moreembodiments, more than one user are separated by code separation.

In one or more embodiments, the method further involves when at leastone atmospheric event occurs, storing, by at least one first processoron at least one first satellite, at least one critical mission parameterof the as-is state of at least one first satellite in memory. In someembodiments, the method further involves when at least one atmosphericevent ends, uploading, by at least one first processor on at least onefirst satellite, at least one critical mission parameter from memory;and configuring, by at least one first processor on at least one firstsatellite, at least one first satellite according to at least onecritical mission parameter.

In one or more embodiments, a system for communications involves atleast one laser on at least one first satellite to transmit at least onefirst transmit signal. The system further involves at least one detectoron least one first satellite to receive at least one first receivesignal. In one or more embodiments, at least one first satellite is insuper-geosynchronous earth orbit (S-GEO). In some embodiments, at leastone first transmit signal and at least one first receive signal arelaser signals. The system further involves at least one first processor,on at least one first satellite, to adapt at least one first transmitsignal according to at least one atmospheric event.

In at least one embodiment, the system further involves at least oneshielding on at least one first satellite for protection from at leastone atmospheric event. In one or more embodiments, the system furtherinvolves at least one telemetry and command (T&C) acquisition sensor onat least one first satellite, where at least one T&C acquisition sensoris radiation hardened. In some embodiments, the system further involvesadaptive optics associated with at least one user, where at least oneuser receives at least one first transmit signal.

In one or more embodiments, a method for communications involvestransmitting, by at least one laser on at least one first satellite, atleast one first transmit signal. The method further involves receiving,by at least one detector on at least one first satellite, at least onefirst receive signal. In one or more embodiments, at least one firstsatellite is in super-geosynchronous Earth orbit (S-GEO). In someembodiments, at least one first transmit signal and at least one firstreceive signal are laser signals and have a field of regard covering onehemisphere of the Earth.

In one or more embodiments, at least one first transmit signal istransmitted towards Earth.

In at least one embodiment, at least one first transmit signal istransmitted towards an airborne vehicle, a terrestrial vehicle, aterrestrial entity, and/or a marine vehicle.

In one or more embodiments, at least one first transmit signal istransmitted towards at least one second satellite. In some embodiments,at least one second satellite is a lower Earth orbiting (LEO) satellite,a medium Earth orbiting (MEO) satellite, a geosynchronous Earth orbiting(GEO) satellite, a highly elliptical Earth orbiting (HEO) satellite,and/or a S-GEO satellite.

In at least one embodiment, at least one first transmit signal and atleast one receive signal have a field of view ranging betweenapproximately 3 to 10 kilometers (km).

In one or more embodiments, the S-GEO is an orbit higher than GEO.

In at least one embodiment, the S-GEO orbit is an orbit approximatelyfive times higher than GEO.

In one or more embodiments, the method further involves transmitting, byat least one transmit antenna on at least one first satellite, at leastone second transmit signal. The method further involves receiving, by atleast one receive antenna on at least one first satellite, at least onesecond receive signal. In some embodiments, at least one second transmitsignal and at least one second receive signal are radio frequency (RF)signals. In at least one embodiment, at least one transmit antenna andat least one receive antenna are the same antenna or different antennas.

In at least one embodiment, at least one first satellite operatesautonomously.

In one or more embodiments, the method further involves gimballing, withat least one first gimbal, at least one laser.

In at least one embodiment, the method further involves gimballing, withat least one second gimbal, at least one detector.

In one or more embodiments, at least one first gimbal and at least onesecond gimbal are the same gimbal or different gimbals.

In at least one embodiment, the method further involves transmitting, byat least one telemetry and command (T&C) laser on at least one firstsatellite, at least one T&C transmit signal. The method further involvesreceiving, by at least one T&C detector on at least one first satellite,at least one T&C receive signal.

In one or more embodiments, a system for communications involves atleast one laser, on at least one first satellite, to transmit at leastone first transmit signal. The system further involves at least onedetector, on at least one first satellite, to receive at least one firstreceive signal. In one or more embodiments, at least one first satelliteis in super-geosynchronous Earth orbit (S-GEO). In some embodiments, atleast one first transmit signal and at least one first receive signalare laser signals and have a field of regard covering one hemisphere ofthe Earth.

The features, functions, and advantages can be achieved independently invarious embodiments of the present disclosure or may be combined in yetother embodiments.

DRAWINGS

These and other features, aspects, and advantages of the presentdisclosure will become better understood with regard to the followingdescription, appended claims, and accompanying drawings where:

FIG. 1 is a diagram showing an exemplary laser communications satellite,to be employed for the disclosed system for laser communications,including a laser/detector, in accordance with at least one embodimentof the present disclosure.

FIG. 2 is a diagram showing an exemplary laser communications satellite,to be employed for the disclosed system for laser communications,including a laser/detector along with a gimbal, in accordance with atleast one embodiment of the present disclosure.

FIG. 3 is a diagram showing an exemplary laser communications satellite,to be employed for the disclosed system for laser communications,including a laser/detector along with a gimbal as well as an antennaalong with a gimbal, in accordance with at least one embodiment of thepresent disclosure.

FIG. 4 is a diagram showing an exemplary laser communications satellite,to be employed for the disclosed system for laser communications,including a laser/detector along with a gimbal as well as a telemetryand command (T&C) laser along with a gimbal, in accordance with at leastone embodiment of the present disclosure.

FIG. 5 is a flow chart depicting a disclosed method for lasercommunications, in accordance with at least one embodiment of thepresent disclosure.

FIG. 6 is a flow chart depicting another disclosed method for lasercommunications, in accordance with at least one embodiment of thepresent disclosure.

FIG. 7 is a diagram showing the orbit geometry for the disclosed systemfor laser communications, in accordance with at least one embodiment ofthe present disclosure.

FIG. 8 is a diagram showing an exemplary launch vehicle configurationthat may be used for a laser communications satellite of the disclosedsystem for laser communications, in accordance with at least oneembodiment of the present disclosure.

FIG. 9 is a diagram showing the disclosed system for lasercommunications, in accordance with at least one embodiment of thepresent disclosure.

DESCRIPTION

The methods and apparatus disclosed herein provide an operative systemfor laser communications in super-geosynchronous Earth orbit (S-GEO).The disclosed system provides an architecture to achieve resiliencyagainst natural (e.g., solar flares) and manmade (e.g., electromagneticinterference (EMI) bursts) threats for a super-geosynchronous (S-GEO)constellation of laser communications satellites by combining a lowprobability of detection lasercom waveform with an equally lowprobability of satellite detection S-GEO orbit.

The constellation preferably comprises three or more satellites in anorbit near the equatorial plane. It should be noted that threesatellites located in a S-GEO orbit that is five times (5×)geosynchronous Earth orbit (GEO) provide global coverage of the Earth.However, in other embodiments, the satellites in the constellation mayorbit in a polar orbit or an inclined orbit. Each satellite providesoptical communications service and optical crosslink services to provideuninterrupted service to users. Multiple satellites may be launched perlaunch vehicle in order to reduce costs. The system optimally includeshybrid radio frequency (RF) services in order to communicate with usersblocked by clouds and users without laser communications terminals.

The present disclosure provides a system for communicating optically(via laser(s)) through the atmosphere following an electromagnetic pulse(EMP) by combining a waveform that is resilient to post-EMP atmosphericeffects (e.g., an optical frequency waveform) with an approach fordetecting an EMP and recovering from the EMP's effects on electronics.The waveform uses an optical wavelength selected to avoid thewavelengths most affected by post-EMP atmospheric effects, a longinterleaver to compensate for fades, and an error correcting code forcorrecting bit errors that occur during fades.

The present disclosure is a combination of employing S-GEO (e.g., fivetimes GEO) for low probability of detection of satellites and resilienceagainst manmade threats plus lasercom links for strategic communicationsthat would avoid probability of detection and interception. In addition,the present disclosure employs laser communications for the purpose ofcommunicating through post-EMP atmospheric effects, which negativelyaffects RF communications. It should be noted that different wavelengths(λ) interact differently with these post-EMP effects. As such, thedisclosed system takes advantage of these properties by employing lasercommunications.

As previously mentioned above, strategic nuclear forces have uniquecommunications requirements, which are: (1) global coverage, (2) near100% availability, (3) long lifetime, (4) low probability ofdetection/interception (LPI/LPD), (5) able to operate without groundintervention, (6) capable of working through challenging atmosphericenvironments, (7) capable of working through post-nuclear atmosphericeffects, (8) resilient to manmade and natural threats, and (9) providingagainst natural threats, such as Van Allen radiation belts, solarstorms, and geomagnetic storms.

Currently, there are a number of communications systems employed andbeing developed. However, these systems do not meet all of therequirements. These systems include, but are not limited to, theMilitary Strategic and Tactical Relay (Milstar) communicationsnetwork/Advanced Extremely High Frequency (AEHF) satellite system, theLunar Laser Communications Demo (LLCD), the Laser CommunicationsResearch Demo (LCRD), and the European Data Relay System (EDRS).Regarding Milstar/AEHF, AEHF satellites are expensive. In addition,since AEHF satellites are in geosynchronous Earth orbit (GEO), they areeasy to detect and track. LLCD demonstrates laser communications betweenthe Earth and the moon. LLCD's space element was placed into lunar orbitand was designed to relay scientific data from the moon to the Earth.Although laser communications is inherently LPI/LPD, and the lunar orbitprovides some resiliency to threats, LLCD does not provide globalcoverage, high availability, long lifetime, or the ability to operatewithout ground intervention. LCRD is a planned GEO satellite beingdeveloped by the National Aeronautics and Space Administration (NASA) asa laser communications technology demonstration. However, LCRD does notprovide global coverage, high availability, long lifetime, or theability to operate without ground intervention. EDRS is a plannedGEO-based satellite system being developed by the European Space Agency(ESA) that utilizes an optical crosslink between two satellites. EDRSdoes not provide global coverage, high availability, long lifetime, orthe ability to operate without ground intervention.

The S-GEO lasercom system meets the requirements for strategic nuclearforces with the following improvements over the existing solutions. Fora first improvement, compared to Milstar/AEHF, laser communicationssystems, which are employed by the present disclosure, require lesssize, weight, and power (SWAP) for a given data rate than a similarradio frequency (RF) communications system. As a result, the strategiclasercom system has lower recurring costs relative to, for example, anAEHF satellite. For a second improvement, compared to Milstar/AEHF,LCRD, LLCD, and EDRS, since laser communication systems provide areduction in size, optionally more than one satellite in the S-GEOlasercom system may be launched on a single launch vehicle, therebylowering launch costs. For a third improvement, compared toMilstar/AEHF, LCRD, and EDRS, satellites in the S-GEO lasercom systemare in a higher altitude orbit than GEO satellites and are smaller thanAEHF satellites. As a result, S-GEO satellites have lower radar andvisible cross sections as measured from the Earth, are more difficult totrack, and are more difficult to deploy countermeasures against. For afourth improvement, compared to Milstar/AEHF, LCRD, and EDRS,optionally, satellites in the S-GEO lasercom system may reach theirfinal orbit by being injected into geosynchronous orbit (GEO) orgeosynchronous transfer orbit (GT) and then by using, for example, ahigh specific impulse, low thrust propulsion system they can transferinto the S-GEO orbit. For a fifth improvement, compared to Milstar/AEHF,laser communications systems user narrower wavelengths than RF systems.These narrow wavelengths result in a smaller beam footprint on theEarth—approximately 3 to 10 kilometers (km)—and make the systemsinherently difficult to detect and intercept. Using lasercommunications, which optionally may include laser telemetry and command(T&C), enables the satellites to remain undetected once they haveexceeded the maximum range of space surveillance systems.

For a sixth improvement, compared to Milstar/AEHF, LCRD, LLCD, and EDRS,optionally, satellites in the S-GEO lasercom system, as a result oftheir small size, may be launched as a secondary satellite in tandemwith a primary satellite, thereby reducing launch costs and increasingthe complexity of tracking their orbits. For a seventh improvement,compared to Milstar/AEHF, LCRD, LLCD, and EDRS, optionally, satellitesin the S-GEO lasercom system may include one or more training satellitesthat would allow operators to train using the system without having topotentially reveal the general location of the operational satellites bypointing at them. For an eighth improvement, compared to LCRD, LLCD, andEDRS, the S-GEO lasercom system has the ability to operate autonomouslywithout ground intervention. For a ninth improvement, compared toMilstar/AEHF, LCRD, LLCD, and EDRS, optionally the S-GEO lasercom systemmay use wavelengths (e.g., optical wavelengths) that can penetrate theocean in order to communicate with undersea users.

For a tenth improvement, compared to LCRD, LLCD, and EDRS, optionally,the S-GEO lasercom system may use hybrid LPI/LPD RF communications inorder to reach users blocked by clouds (i.e. optical wavelengths havedifficulty passing through clouds) and users that do not have lasercommunications terminals. Although this option will increase the SWAP ofthe satellites, they will be difficult to detect and track, especiallyif they refrain from using RF communications until needed. For aneleventh improvement, compared to LCRD and LLCD, optionally, the S-GEOlasercom system may use crosslinks (e.g., optical and/or RF crosslinks)to interconnect the satellites of the constellation. For a twelfthimprovement, compared to LCRD and LLCD, optionally, the S-GEO lasercomsystem may service multiple users per beam by separating userspectrally. For a thirteenth improvement, compared to LCRD and LLCD,optionally, the S-GEO lasercom system may service multiple users perbeam by separating users temporally.

For a fourteenth improvement, compared to LLCD and LCRD, the strategiclasercom system uses a wavelength (e.g., a wavelength range) (e.g., anoptical wavelength range) selected to avoid the wavelengths (e.g., RFwavelengths) most affected by post-EMP atmospheric effects. For afifteenth improvement, compared to LLCD and LCRD, optionally, thestrategic lasercom system employs additional shielding to protectelectronics form the effects of an EMP. For a sixteenth improvement,compared to LLCD and LCRD, optionally, the strategic lasercom systememploys radiation hardened telemetry and command (T&C) acquisitionsensors to allow them to operate following an EMP. For a seventeenthimprovement, compared to LLCD and LRCD, the strategic lasercom systememploys adaptive optics (e.g., deformable mirrors) in ground terminalsto compensate for post-EMP atmospheric effects. For an eighteenthimprovement, compared to LLCD and LCRD, optionally, the strategiclasercom system may use adjustable long interleavers designed tomitigate the effects of long fades caused by post-EMP atmosphericeffects.

In the following description, numerous details are set forth in order toprovide a more thorough description of the system. It will be apparent,however, to one skilled in the art, that the disclosed system may bepracticed without these specific details. In the other instances, wellknown features have not been described in detail so as not tounnecessarily obscure the system.

Embodiments of the present disclosure may be described herein in termsof functional and/or logical components and various processing steps. Itshould be appreciated that such components may be realized by any numberof hardware, software, and/or firmware components configured to performthe specified functions. For example, an embodiment of the presentdisclosure may employ various integrated circuit components, e.g.,memory elements, digital signal processing elements, logic elements,look-up tables, or the like, which may carry out a variety of functionsunder the control of one or more microprocessors or other controldevices. In addition, those skilled in the art will appreciate thatembodiments of the present disclosure may be practiced in conjunctionwith other components, and that the system described herein is merelyone example embodiment of the present disclosure.

For the sake of brevity, conventional techniques and components relatedto laser communication systems, and other functional aspects of thesystem (and the individual operating components of the systems) may notbe described in detail herein. Furthermore, the connecting lines shownin the various figures contained herein are intended to representexample functional relationships and/or physical couplings between thevarious elements. It should be noted that many alternative or additionalfunctional relationships or physical connections may be present in anembodiment of the present disclosure.

FIG. 1 is a diagram showing an exemplary laser communications satellite100, to be employed for the disclosed system for laser communications,including a laser/detector 120, in accordance with at least oneembodiment of the present disclosure. In this figure, a satellite 100 isshown having a laser/detector unit 120 mounted onto the bus 110. Thelaser/detector unit 120 comprises a laser for transmission of opticalsignals and a detector for reception of optical signals. It should benoted that in other embodiments, the laser and the detector may comprisetwo separate units rather than one laser/detector unit 120 as is shownin FIG. 1. In one or more embodiments, shielding is employed over atleast a portion (e.g., the electronics) of the satellite 100 to shieldat least a portion of the satellite 100 from atmospheric events.

During operation of the disclosed system, the satellite 100 orbits theEarth in S-GEO. S-GEO is defined as being an orbit higher than GEO. Inone or more embodiments, GEO is a circular orbit of 35,786 kilometers(km) above the Earth's equator and following the direction of theEarth's rotation. However, it should be noted that in other embodiments,GEO may be at an inclined orbit instead of following the Earth'sequator. In some embodiments of the present disclosure, S-GEO orbit isapproximately five times higher than GEO (e.g., 5*35,786 km=178,930 km).However, it should be noted that S-GEO may be any orbit higher than GEO,such as two times higher than GEO, 2.5 times higher than GEO, threetimes higher than GEO, four times higher than GEO, etc. Also, duringoperation of the disclosed system, the laser of the laser/detector 120of the satellite 100 will transmit at least one transmit signal 130 to atarget (e.g., another satellite, a vehicle, entity or Earth) 150, andthe detector of the laser/detector 120 will receive at least one receivesignal 140 from the target 150. The transmit signal(s) 130 and thereceive signal(s) 140 are laser signals (i.e. signals having opticalfrequencies and wavelengths) and have a field of regard covering onehemisphere of the Earth (refer to FIG. 7).

In some embodiments, during operation of the disclosed system, the laserof the laser/detector 120 transmits at least one transmit signal 130towards a vehicle and/or entity on Earth, and the detector of thelaser/detector 120 receives at least one receive signal 140 back fromthe vehicle and/or entity on Earth. The vehicle may be an airbornevehicle, a terrestrial vehicle, or a marine vehicle. The airbornevehicle may be, for example, a satellite, a space plane, or an aircraft.The terrestrial vehicle may be, for example, a train, truck, car, ortank. And, the marine vehicle may be, for example, a submarine, a ship,or a boat. The entity may be a terrestrial ground station or a mobileuser device.

In at least one embodiment, during operation of the disclosed system,the satellite 100 communicates via a crosslink with another satellite(not shown). For these embodiments, the laser of the laser/detector 120transmits at least one transmit signal 130 towards the other satellite,and the detector of the laser/detector 120 receives at least one receivesignal 140 back from the other satellite. In one or more embodiments,the other satellite is a lower Earth orbit (LEO) satellite, a mediumEarth orbit (MEO) satellite, a geosynchronous Earth orbit (GEO)satellite, a highly elliptical Earth orbit (HEO) satellite, or asuper-geosynchronous Earth orbit (S-GEO) satellite.

In one or more embodiments, during operation of the disclosed system, atleast one processor (not shown) on the satellite 100 monitors the linkperformance by monitoring the bit error rate (and/or the signalstrength) of at least one receive signal 140 received by the detector ofthe laser/detector 120. It should be noted that in other embodiments,other link attributes other than (or in addition to) the bit error rateand/or the signal strength may be monitored. At least one processor thendetermines whether at least one atmospheric event has occurred using thebit error rate (and/or the signal strength). For example, if theprocessor(s) determines that the bit error rate is above a certainpredetermined bit error rate threshold (and/or that the signal strengthis below a certain predetermined signal strength threshold), then theprocessor(s) may determine that at least one atmospheric event hasoccurred. Types of atmospheric events that may be determined to haveoccurred are manmade events (e.g., EMI, EMP, a nuclear environment) ornatural events (e.g., solar flares). After the processor(s) hasdetermined that at least one atmospheric event has occurred, theprocessor(s) then adapts at least one transmit signal 130 according tothe atmospheric event(s). At least one transmit signal 130 may beadapted by adapting the transmit signal's 130 interleavers, codecs, datarate, and/or modulation format.

Regarding interleavers and codecs, in one or more embodiments, at leastone transmit signal employs interleavers and/or codecs. Interleavers andcodecs are typically used in signals to mitigate optical channel fadingcaused by atmospheric conditions. A nuclear scintillating environmenthas the potential to cause additional fading due to the ionizingradiation potentially affecting the atmosphere. In at least oneembodiment, during operation of the disclosed system, at least oneprocessor on the satellite 100 adapts at least one transmit signal 130to contain longer interleavers than the current interleavers (i.e.contain interleavers with longer lengths than the lengths of the currentinterleavers), for example by increasing the interleaver delay, in orderto compensate for the atmospheric event(s). Types of interleavers thatmay be employed include, but are not limited to, block interleavers andconvolutional interleavers. In some embodiments, during operation of thedisclosed system, at least one processor on the satellite 100 adapts thetransmit signal to contain codecs (e.g., a Turbo Product Code and LowDensity Parity Check Code) with an increase in redundancy (i.e. bydecreasing the code rate) in order to compensate for the atmosphericevent(s). Using interleavers and codecs that are adaptable to theenvironmental conditions would allow for communications to continue, forexample, after a nuclear event.

Regarding the data rate, in at least one embodiment, during operation ofthe disclosed system, at least one processor on the satellite 100 adaptsat least one transmit signal 130 to have a slower data rate in order tocompensate for the atmospheric event(s). With regard to the modulationformat, in some embodiments, at least one processor on the satellite 100adapts at least one transmit signal 130 by modifying the modulationformat to a more robust waveform (e.g., quadrature phase shift keying(QPSK), binary phase shift keying (BPSK), pulse position modulation(PPM)) in order to compensate for the atmospheric event(s).

After at least one transmit signal 130 is adapted, if the processor(s)determines that the bit error rate is still above the predetermined biterror rate threshold (and/or the signal strength is still below thepredetermined signal strength threshold), the processor(s) will furtheradapt at least one transmit signal 130. The processor(s) will continueto further adapt at least one transmit signal 130 until the processor(s)determines that the bit error rate is no longer above the bit error ratethreshold (and/or the signal strength is no longer below thepredetermined signal strength threshold).

In some embodiments, during operation of the disclosed system, at leastone user processor (not shown) associated with a user (or target 150),associated with a vehicle or an entity, monitors the link performance bymonitoring (either continuously or intermittently) the bit error rate(and/or the signal strength) of at least one transmit signal 130received by the user (or target) 150. At least one user processor thendetermines whether at least one atmospheric event has occurred using thebit error rate (and/or the signal strength). After the user processor(s)has determined that at least one atmospheric event has occurred, theuser processor(s) then sends a message via at least one receive signal140 to the satellite 100 to adapt at least one transmit signal 130(e.g., by adapting the transmit signal's 130 interleavers, codecs, datarate, and/or modulation format) according to the atmospheric event(s).Then, after the laser of the laser/detector 120 of the satellite 100receives the message in at least one receive signal 140, at least oneprocessor on the satellite 110 adapts at least one transmit signal 130according to the atmospheric event(s). After at least one transmitsignal 130 is adapted, the user processor(s) associated with the usermonitors the link performance by monitoring (either continuously orintermittently) the bit error rate (and/or the signal strength) of atleast one transmit signal 130 received by the user (or target) 150. Ifthe user processor(s) associated with the user determines that the biterror rate is still above the predetermined bit error rate threshold(and/or the signal strength is still below the predetermined signalstrength threshold), the processor(s) on the satellite 100 will furtheradapt at least one transmit signal 130. The processor(s) on thesatellite 100 will continue to further adapt at least one transmitsignal 130 until the user processor(s) associated with the userdetermines that the bit error rate is no longer above the bit error ratethreshold (and/or the signal strength is no longer below the signalstrength threshold).

In some embodiments, at least one processor (either on the satellite 100or associated with a user) may monitor radiation data from a nucleardetector, on the satellite 100 or associated with the user, for anuclear event. For example, if the processor(s) (on the satellite 100 orassociated with a user) determines that the radiation level is above acertain predetermined radiation level threshold, then the processor(s)(on the satellite 100 or associated with a user) may determine that anuclear event has occurred. At least one transmit signal 130 will beadapted (e.g., by adapting the transmit signal's 130 interleavers,codecs, data rate, and/or modulation format) by the processor(s) on thesatellite 100 according to the severity of the radiation data, when theprocessor(s) (either on the satellite 100 or associated with a user) hasdetermined from the radiation data from the nuclear detector that anuclear event has occurred.

In one or more embodiments, individual targets (or users) are separated(or isolated) from one another in the receive field of view by variousdifferent techniques. One technique is an in-aperture spatial separationof users. For this technique, for example, a physical grid of areas ofthe aperture plane may be used to separate users for identification.Another technique is spectral separation, where different wavelengthsmay be assigned per user such that each user has a unique wavelength(s).Yet another technique is polarization separation, where one user isassigned one polarization (e.g., horizontal polarization or left handcircular polarization) and a different user is assigned the orthogonalpolarization (e.g., vertical polarization or right hand polarization).And another technique is temporal separation, where each of the usersare assigned different time slots (e.g., time division multiple access(TDMA)). Yet another technique is code separation, where each of theusers are assigned a different code (e.g., code division multiple access(CDMA)).

In one or more embodiments, during operation of the disclosed system,after at least one processor (associated with the user and/or with thesatellite) determines that at least one atmospheric event (e.g., manmadeevents (e.g., EMI, EMP, a nuclear environment) or natural events (e.g.,solar flares)) has occurred by, for example, monitoring the bit errorrate (and/or the signal strength) of the transmit signal 130 and/ormonitoring radiation data from a nuclear detector, at least oneprocessor associated with the satellite will begin a shutdown sequencefor the satellite. The shutdown sequence is used to safe the satelliteduring the atmospheric event and to allow for the satellite to be ableto quickly recover after the atmospheric event ends autonomously. At thestart of the shutdown sequence, the satellite processor(s) storescritical mission parameters of the as-is state of the satellite prior tothe atmospheric event by rapidly writing the critical mission parametersto memory (e.g., non-volatile triple redundant memory). Critical missionparameters may include, but are not limited to, gimbal angles, beamsteerer positions, critical configuration constants, and time. After theatmospheric event ends, upon restart, the satellite processor(s) rapidlyuploads the critical mission parameters from memory. Then, the satelliteprocessor(s) configures the satellite according to the critical missionparameters to allow for recovery.

FIG. 2 is a diagram showing an exemplary laser communications satellite200, to be employed for the disclosed system for laser communications,including a laser/detector 230 along with a gimbal 220, in accordancewith at least one embodiment of the present disclosure. In this figure,a satellite 200 is shown having a laser/detector unit 220 mounted ontothe bus 210. The laser/detector unit 220 comprises a laser fortransmission of optical signals and a detector for reception of opticalsignals. A gimbal 220 is mounted onto the bus 210 and is used to gimbal(i.e. rotate, e.g., in azimuth and/or elevation) the laser/detector unit220.

FIG. 3 is a diagram showing an exemplary laser communications satellite300, to be employed for the disclosed system for laser communications,including a laser/detector 340 along with a gimbal 330 as well as anantenna 350 along with a gimbal 320, in accordance with at least oneembodiment of the present disclosure. In this figure, a satellite 300 isshown having a laser/detector unit 340 mounted onto the bus 310. Thelaser/detector unit 340 comprises a laser for transmission of opticalsignals and a detector for reception of optical signals. A gimbal 330 ismounted onto the bus 310 and is used to gimbal (i.e. rotate) thelaser/detector unit 340.

Also in FIG. 3, the satellite 300 is shown having an antenna (i.e. areflector antenna) 350 mounted onto the bus 310. The antenna 350comprises a reflector for transmitting RF signals and for receiving RFsignals. It should be noted that in other embodiments, the antenna 350may comprise two separate units (e.g., a transmit reflector antenna anda receive reflector antenna) rather than one antenna 350 as is shown inFIG. 3. In addition, a gimbal 320 is mounted onto the bus 310 and isused to gimbal (i.e. rotate, e.g., in azimuth and elevation) the antenna350. It should be noted that, during operation, the antenna 350 maytransmit and receive RF signals to and from another satellite.

FIG. 4 is a diagram showing an exemplary laser communications satellite400, to be employed for the disclosed system for laser communications,including a laser/detector 450 along with a gimbal 420 as well as atelemetry and command (T&C) laser 440 along with a gimbal 430, inaccordance with at least one embodiment of the present disclosure. Inthis figure, a satellite 400 is shown having a laser/detector unit 450mounted onto the bus 410. The laser/detector unit 450 comprises a laserfor transmission of optical signals and a detector for reception ofoptical signals. A gimbal 420 is mounted onto the bus 410 and is used togimbal (i.e. rotate, e.g., in azimuth and elevation) the laser/detectorunit 450.

Also in FIG. 4, the satellite 400 is shown having a T&C laser 440mounted onto the bus 410. The T&C laser 440 transmits T&C transmitsignals and receives T&C receive signals. It should be noted that inother embodiments, the T&C laser 440 may comprise two separate units(e.g., a transmit laser and a receive detector) rather than one T&Claser 440 as is shown in FIG. 4. In addition, a gimbal 430 is mountedonto the bus 410 and is used to gimbal (i.e. rotate, e.g., in azimuthand elevation) the T&C laser 440. In one or more embodiments, the T&Claser 440 includes an acquisition sensor. In some embodiments, the T&Cacquisition sensor is radiation hardened.

FIG. 5 is a flow chart depicting a disclosed method 500 for lasercommunications, in accordance with at least one embodiment of thepresent disclosure. At the start 510 of the method 500, at least onelaser, on at least one first satellite, transmits at least one firsttransmit signal 520. At least one detector, on at least one firstsatellite, then receives at least one first receive signal 530. At leastone optional transmit antenna, on at least one first satellite,transmits at least one second transmit signal 540. Then, at least oneoptional receive antenna, on at least one first satellite, receives atleast one second receive signal 550. Then, the method 500 ends 560.

FIG. 6 is a flow chart depicting another disclosed method 600 for lasercommunications, in accordance with at least one embodiment of thepresent disclosure. At the start 610 of the method 600, at least onelaser, on at least one first satellite, transmits at least one firsttransmit signal 620. At least one detector, on at least one firstsatellite, then receives at least one first receive signal 630. At leastone first processor, on at least one first satellite, monitors a linkperformance of at least one first receive signal and/or radiation data640. Then, at least one first processor, on at least one firstsatellite, determines whether at least one atmospheric event hasoccurred using the link performance and/or the radiation data 650. Atleast one first processor, on at least one first satellite, adapts atleast one first transmit signal according to the atmospheric event 660.Then, the method 600 ends 670.

FIG. 7 is a diagram showing the orbit geometry 700 for the disclosedsystem for laser communications, in accordance with at least oneembodiment of the present disclosure. In this figure, three lasercommunications satellites 710, 720, 730 are shown to be orbiting theEarth 750 at a S-GEO orbit 740. It should be noted that S-GEO orbit 740,being at a very high orbit, allows for a low probability of detection ofsatellites and interception of signals, and allows for resilienceagainst manmade threats (e.g., EMP).

When S-GEO 740 is five times higher than GEO 760, the Earth's 750angular subtense is about 3 to 3.5 degrees (i.e. the field of regard).Typically, it is very difficult to have large apertures and large fieldof views in a single laser communications system that is small enough tofield on a satellite. Using S-GEO 740 (i.e. at five times GEO orbit 760)coupled with a modest data rate allows for a moderately sized apertureand a moderately sized viewfield. As such, as shown in FIG. 7, at S-GEO740 (i.e. at five times GEO orbit 760), only three satellites 710, 720,730 (with each using only a single laser communications aperture) areneeded to obtain full Earth coverage.

Also shown in this figure, in one or more embodiments, the satellites710, 720, 730 may reach their final S-GEO orbit 740 by being injectedinto GEO orbit 760 or geosynchronous transfer orbit (GT) 770 and then byusing, for example, a high specific impulse, low thrust propulsionsystem they can transfer into the S-GEO orbit 740.

FIG. 8 is a diagram showing an exemplary launch vehicle configuration800 that may be used for a laser communications satellite of thedisclosed system for laser communications, in accordance with at leastone embodiment of the present disclosure. In this figure, two lasercomsatellites 810, 820 (i.e. secondary satellite #1 and secondary satellite#2), which are compact in size, are shown to be housed in tandem alongwith a larger satellite (e.g., a RF commercial communications satellite)830 (i.e. primary satellite) in a single launch vehicle fairing 840.Since lasercom satellites 810, 820 are small in size, multiplesatellites may be launched per launch vehicle fairing 840, therebyallowing for a reduction in launch costs. It should be noted that, inother embodiments, various different combinations of lasercomsatellite(s) 810, 820 and/or larger satellite(s) 830 can be housedtogether in a launch vehicle (e.g., three lasercom satellites may behoused with one larger satellite), depending upon the launch vehiclefairing 840 capacity and the satellite sizes.

FIG. 9 is a diagram showing the disclosed system 900 for lasercommunications, in accordance with at least one embodiment of thepresent disclosure. In this figure, four lasercom satellites 910 a, 910b, 910 c, 910 d are shown to be orbiting Earth 920 at S-GEO. Crosslinks(e.g., laser communications and/or RF communications) 930 a, 930 b, 930c, 930 d are shown to be between the lasercom satellites 910 a, 910 b,910 c, 910 d. Satellite 910 a is a lasercom satellite that is operatingautonomously.

Satellite 910 b is a lasercom satellite that is a hybrid RF satellite(refer to FIG. 3). Satellite 910 b is shown to be transmitting andreceiving RF signals 950 to and from a legacy RF terminal 940 on Earth920. Satellite 910 c is shown to be transmitting and receiving opticalsignals 960 to and from an undersea user (e.g., a submarine) 970.

Also in this figure, satellite 910 d is shown to be transmitting andreceiving optical signals to and from multiple user terminals 980 withinthe beam 990. It should be noted that the beam field of view isapproximately 3 to 10 kilometers (km). In one or more embodiments, auser terminal 980 may, for example, include adaptive optics (e.g.,deformable mirrors) to compensate for spatial phase perturbations oflight caused by post-EMP atmospheric effects. Additionally, in thisfigure, a terminal (e.g., a space surveillance terminal) 993 is shown tobe outside of the narrow beam 990. In one or more embodiments, theterminal 993, outside of the beam 990, may be an adversary groundstation attempting to intercept the beam 990.

This figure also shows a satellite 995 orbiting Earth at GEO. Lasercomsatellite 910 d is shown to be transmitting and receiving opticalsignals 997 to and from satellite 995.

It should be noted that, as previously mentioned, lasercom satellites910 a, 910 b, 910 c, 910 d may be transmitting and receiving signals toand from various different vehicles (e.g., airborne, terrestrial, andmarine) and/or various different entities (e.g., airborne, terrestrial,and marine). FIG. 9 presents only some of the many possiblecommunication scenarios for the disclosed system 900.

Although particular embodiments have been shown and described, it shouldbe understood that the above discussion is not intended to limit thescope of these embodiments. While embodiments and variations of the manyaspects of the present disclosure have been disclosed and describedherein, such disclosure is provided for purposes of explanation andillustration only. Thus, various changes and modifications may be madewithout departing from the scope of the claims.

Where methods described above indicate certain events occurring incertain order, those of ordinary skill in the art having the benefit ofthis disclosure would recognize that the ordering may be modified andthat such modifications are in accordance with the variations of thepresent disclosure. Additionally, parts of methods may be performedconcurrently in a parallel process when possible, as well as performedsequentially. In addition, more parts or less part of the methods may beperformed.

Accordingly, embodiments are intended to exemplify alternatives,modifications, and equivalents that may fall within the scope of theclaims.

Although certain illustrative embodiments and methods have beendisclosed herein, it can be apparent from the foregoing disclosure tothose skilled in the art that variations and modifications of suchembodiments and methods can be made without departing from the truespirit and scope of the art disclosed. Many other examples of the artdisclosed exist, each differing from others in matters of detail only.Accordingly, it is intended that the art disclosed shall be limited onlyto the extent required by the appended claims and the rules andprinciples of applicable law.

We claim:
 1. A method for communications, the method comprising:transmitting, by at least one laser on at least one first satellite, atleast one first transmit signal; receiving, by at least one detector onthe at least one first satellite, at least one first receive signal,wherein the at least one first transmit signal and the at least onefirst receive signal are laser signals; adapting, by at least one firstprocessor on the at least one first satellite, the at least one firsttransmit signal according to at least one atmospheric event; when the atleast one atmospheric event occurs, storing, by the at least one firstprocessor on the at least one first satellite, at least one criticalmission parameter of an as-is state of the at least one first satellitein memory; and when the at least one atmospheric event ends, uploading,by the at least one first processor on the at least one first satellite,the at least one critical mission parameter from the memory, andconfiguring, by the at least one first processor on the at least onefirst satellite, the at least one first satellite according to the atleast one critical mission parameter.
 2. The method of claim 1, whereinthe at least one atmospheric event is at least one of a natural event ora manmade event.
 3. The method of claim 2, wherein the natural event isa solar flare.
 4. The method of claim 2, wherein the manmade event is anelectromagnetic pulse (EMP).
 5. The method of claim 1, wherein the atleast one first satellite is in super-geosynchronous earth orbit(S-GEO).
 6. The method of claim 1, wherein the at least one firsttransmit signal employs interleavers, and the interleavers are adaptableaccording to the at least one atmospheric event.
 7. The method of claim1, wherein the at least one first transmit signal employs codecs, andthe codecs are adaptable according to the at least one atmosphericevent.
 8. The method of claim 1 wherein a data rate of the at least onefirst transmit signal is adaptable according to the at least oneatmospheric event.
 9. The method of claim 1, wherein the at least onefirst transmit signal is modulated, and a modulation format of the atleast one first transmit signal is adaptable according to the at leastone atmospheric event.
 10. The method of claim 1, wherein the methodfurther comprises: monitoring, with the at least one first processor onthe at least one first satellite, at least one of link performance ofthe at least one receive signal or radiation data; determining, with theat least one first processor on the at least one first satellite,whether the at least one atmospheric event has occurred using at leastone of the link performance or the radiation data.
 11. The method ofclaim 1, wherein the method further comprises: monitoring, with the atleast one second processor associated with at least one user, at leastone of link performance of the at least one transmit signal or radiationdata; determining, with the at least one second processor associatedwith at least one user, whether the at least one atmospheric event hasoccurred using at least one of the link performance or the radiationdata.
 12. The method of claim 1, wherein the method further comprisesreceiving, by at least one user, the at least one first transmit signal.13. The method of claim 12, wherein more than one of the at least oneuser are separated by spatial separation.
 14. The method of claim 12,wherein more than one of the at least one user are separated by spectralseparation.
 15. The method of claim 12, wherein more than one of the atleast one user are separated by polarization separation.
 16. The methodof claim 12, wherein more than one of the at least one user areseparated by temporal separation.
 17. The method of claim 12, whereinmore than one of the at least one user are separated by code separation.18. A system for communications, the system comprising: at least onelaser on at least one first satellite to transmit at least one firsttransmit signal; at least one detector on the least one first satelliteto receive at least one first receive signal, wherein the at least onefirst transmit signal and the at least one first receive signal arelaser signals; and at least one first processor, on the at least onefirst satellite, to adapt the at least one first transmit signalaccording to at least one atmospheric event; when the at least oneatmospheric event occurs, to store at least one critical missionparameter of an as-is state of the at least one first satellite inmemory; and when the at least one atmospheric event ends, to upload theat least one critical mission parameter from the memory and to configurethe at least one first satellite according to the at least one criticalmission parameter.
 19. The system of claim 18, wherein the systemfurther comprises at least one shielding on the at least one firstsatellite for protection from the at least one atmospheric event. 20.The system of claim 18, wherein the system further comprises at leastone telemetry and command (T&C) acquisition sensor on the at least onefirst satellite, wherein the at least one T&C acquisition sensor isradiation hardened.
 21. The system of claim 18, wherein the systemfurther comprises adaptive optics associated with at least one user,wherein the at least one user receives the at least one first transmitsignal.